Intestinal parasitic infections in man: a review

Intestinal parasites of importance to man are Enterobius vermicularis, the soil-transmitted helminthes (STH)--Ascaris lumbricoides Tricburis trichiura, bookworms (Necator americans/Ancylostoma duodenale) and Strongyloides stercoralis and the protozoa Entamoeba histolytica and Giardia duodenalis. Other protozoa such as Cryptosporidium sp. and Isopora sp. are becoming important in causing prolonged diarrhea in immunocompromised patients. It is estimated that almost 1 billion, 500 million and 900 million people worldwide are infected by the major nematode species--A. lumbricoides, T. trichiura and hookworms respectively. Most of the infections are endemic and widely distributed throughout poor and socio-economically deprived communities in the tropics and subtropics. Environmental, socio-economic, demographic and health-related behavior is known to influence the transmission and distribution of these infections. In giardiasis, one study indicates that age < or = 12 years and the presence of family members infected with Giardia were risk factors for infection. Most of the infections occur in children and both genders are equally affected. Epidemiological studies of STH infections have shown that the prevalence and intensity of infection are highest among children 4-15 years of age. The frequency of distribution of STH infections is over-dispersed and highly aggregated. areas reinfection can occur as early as 2 months post-treatment, and by 4 months, almost half of the population treated become reinfected. By 6 months the intensity of infection was similar to pretreatment level.